Water & wastewater treatment
Wastewater is water that has been used and must be treated before it is released into another body of water so that it does not cause further pollution of water sources. Wastewater comes from a variety of sources. Everything that you flush down your toilet or rinse down the drain is wastewater. Rainwater and runoff, along with various pollutants, go down street gutters and eventually end up at a wastewater treatment facility. Wastewater can also come from agricultural and industrial sources. Some wastewaters are more difficult to treat than others; for example, industrial wastewater can be difficult to treat, whereas domestic wastewater is relatively easy to treat (though it is increasingly difficult to treat domestic waste, due to increased amounts of pharmaceuticals and personal care products that are found in domestic wastewater.
WHO IS RESPONSIBLE FOR MAKING SURE THAT WASTEWATER IS TREATED PROPERLY?
Similar to drinking water provisions, the Karnataka government has delegated responsibility for wastewater treatment to the provinces and territories. There are two federal acts, however, that may apply to wastewater. The Fisheries Act prohibits the release of harmful substances into waters that fish live in. The Indian Environmental Protection Act governs the release of toxic substances into the environment and allows the federal government to develop regulations for the use of toxic substances.
Most provincial and territorial governments have legislation regarding wastewater treatment standards and requirements. Operators of wastewater treatment facilities must obtain permits or licenses from the provincial or territorial government, and these permits may also require additional treatments or limits on effluent discharges. For example, in British Columbia, all municipalities are required to have a Liquid Waste Management Plan; without an approved plan, discharges are illegal. Provincial and territorial governments generally assist municipal governments with funds to build and maintain infrastructure. Municipal governments directly oversee the wastewater treatment process and are able to pass additional by-laws. For example, the Regional Municipality of Ottawa-Carleton has developed a program to eliminate toxic substances from the wastewater treatment system, requiring all industrial, institutional, and commercial facilities to limit the number of certain pollutants that are allowed into sewers.
Operation and maintenance of sewage treatment plant
There are several levels of wastewater treatment; these are primary, secondary, and tertiary levels of treatment.
Most municipal wastewater treatment facilities use primary and secondary levels of treatment, and some also use tertiary treatments. The type and order of treatment may vary from one treatment plant to another, but this diagram of the Ottawa-Carleton wastewater treatment plant illustrates the basic components.
Typical Urban Wastewater Treatment Plant
The primary level of treatment uses screens and settling tanks to remove the majority of solids. This step is extremely important because solids make up approximately 35 percent of the pollutants that must be removed. The screens usually have openings of about 10 millimeters, which is small enough to remove sticks, garbage, and other large materials from the wastewater. This material is removed and disposed of at the landfill.
The water is then put into settling tanks (or clarifiers), where it sits for several hours, allowing the sludge to settle and a scum to form on the top. The scum is then skimmed off the top, the sludge is removed from the bottom, and the partially treated wastewater moves on to the secondary treatment level. The primary treatment generally removes up to 50 percent of the Biological Oxygen Demand (BOD; these are substances that use up the oxygen in the water), around 90 percent of suspended solids, and up to 55 percent of fecal coliforms. While primary treatment removes a significant amount of harmful substances from wastewater, it is not enough to ensure that all harmful pollutants have been removed.
Secondary treatment of wastewater uses bacteria to digest the remaining pollutants. This is accomplished by forcefully mixing the wastewater with bacteria and oxygen. The oxygen helps the bacteria to digest the pollutants faster. The water is then taken to settling tanks where the sludge again settles, leaving the water 90 to 95 percent free of pollutants. The picture below shows the settling tanks in the Winnipeg Wastewater Treatment Plant. Secondary treatment removes about 85 to 90 percent of BOD and suspended solids, and about 90 to 99 percent of coliform bacteria.